Process Hazard Analysis (PHA) | HAZOP
The first step in the process safety lifecycle is to make the risks of the process visible by means of a Process Hazard Analysis (PHA). We do this “high over” with a HAZID or SWIFT study or extended with a HAZOP study:
– HAZID (HAZard IDentification)
HAZID (HAZard IDentification) is a technique for early identification of potential hazards and threats. The study method is a combination of identification, analysis and brainstorming based on the hazards identified on the checklist. The main benefit of HAZID is that early identification and assessment of critical HSE hazards provides essential input for project development decisions. This will result in safer and more cost-effective design options being adopted with minimal cost of change.
HAZID emphasises the use of the checklist as an opportunity for the team to brainstorm. The knowledge and creativity of the team is used to identify credible causes and thus the applicability of the hazards. It is important that the list of hazards is used creatively and not as a rigid checklist. Only in this way can new or unusual hazards be identified, or specific combinations of factors be identified as causes for concern.
The HAZID checklist is comprehensive but not exhaustive. The team should also be prepared to use the brainstorming process to identify specific new or unforeseen resources. After discussing the overall issues, the team can sharpen the focus of the research and the development can be broken down into a number of clearly defined areas. During the study, all hazards identified by the team are noted and described on a HAZID worksheet. The HAZID study minutes are structured to provide a solid basis for the subsequent transfer of appropriate information.
– SWIFT (Structured What-If Technique)
is a simple alternative to the HAZOP method. You can use the SWIFT for small changes in the plant (MOC, management of change) or in the concept phase of a project, for example. With this method, you can easily bring the highest risks to the surface. You can then include measures to reduce these risks in your design phase.
The Structured What If Checklist (SWIFT) is a thorough, systematic, multidisciplinary team-oriented analysis technique. The Structured What-If Checklist (SWIFT) study technique was developed as an efficient alternative to HAZOP to provide highly effective hazard identification when it can be demonstrated that conditions do not justify the accuracy of a HAZOP. SWIFT can also be used in conjunction with or as a complement to a HAZOP.
How does the SWIFT technique differ from HAZOP?
HAZOP examines the system pipe by pipe, vessel by vessel, etc. SWIFT, on the other hand, is a system-oriented technique that examines entire systems or subsystems, and is therefore fundamentally different from HAZOP. To ensure comprehensive hazard identification, SWIFT relies on a structured brainstorming by a team of experienced process experts with additional questions from a checklist.
Both SWIFT and HAZOP require the input of a team of process experts to evaluate the impact of hazards that may result from various potential failures or errors that they have identified.
In answering all questions asked about realistic deviations from the normal intended operation of a process unit, the team assesses the likelihood of an incident, its possible consequences and the adequacy of precautions to prevent or mitigate it if it occurs. The “What-if?” questions, which can be asked by any team member (including the team leader and recorder), are structured in different categories.
When the team is no longer able to identify additional questions in a category, a category-specific checklist is consulted to elicit additional ideas and ensure completeness.
The technique is efficient because it generally avoids lengthy discussions of areas where the hazards are well understood or where previous analysis has shown that no hazards exist. Its effectiveness in identifying hazards comes from asking questions in several key areas, according to a structured plan, to ensure that all the different types of malfunction or error that are likely to result in a hazard within the system under investigation are fully covered. The SWIFT analysis is further strengthened by the use of checklists at the end of each question category, resulting in additional thoroughness.
– HAZOP (HAZard and OPerability study)
is an extensive study in which you describe scenarios that deviate from the normal situation using fixed guide words. What is the cause of a deviation and what is the consequence? For example, the scenario “high pressure”. The cause is that a valve is closed and the consequence is that the design pressure of a reactor is exceeded, resulting in the release of a large quantity of flammable substance. Without control measures (the naked risk or unmitigated risk), this can lead to one or more injuries or worse. Next, you discuss which independent protection layers you have in place and whether this is sufficient to achieve an acceptable risk.
An important starting point for a HAZOP is the use of the risk matrix. This usually shows the probability on the x-axis and the severity of a deviant situation on the y-axis.
The question is what is an acceptable risk?
Serious process safety incidents are fortunately not very common. The highest risks that we as a society accept, in this case the probability of a fatal accident, are numbers that are difficult to grasp in themselves. One fatality per 100,000 years is a guideline often used in risk studies. Sounds like: this will not happen in my lifetime…
Globally, there are about 9 million workers in the Netherlands who all have the chance to die once every 100,000 years from a non-natural cause at work. That comes down to 90 deaths per year (!) (90 deaths per 9,000,000 workers per year = 1 death per 100,000 years). That is 90 too many. And 90 suddenly sounds very different from once every 100,000 years. And process safety incidents lead not only to personal injury but also to damage to the environment and to the installations themselves (financial risk). No reason to sit still. A HAZOP study helps enormously in mapping this out.
But you can’t keep investing in safety indefinitely. At a certain point, the costs no longer outweigh the benefits. This point is called ALARP: As Low As Reasonably Practicable
